Recycle of vulcanized fluorinated elastomers

ABSTRACT

Compositions and techniques useful to effectively recycle crosslinked (i.e., vulcanized or cured) fluoroelastomers are disclosed. The invention utilizes an additive system that includes a cure-enhancing additive, a crosslinking agent, and an accelerator.

[0001] This application claims priority from U.S. Ser. No. 60/036,230,filed Mar. 12, 1997.

FIELD OF THE INVENTION

[0002] This invention relates to recycling of fluorinated elastomersthat have been at least partially vulcanized.

BACKGROUND OF THE INVENTION

[0003] Fluorinated elastomeric materials (sometimes referred tohereinafter either as fluorinated elastomers or fluoroelastomers) aresynthetic, noncrystalline polymers which are usually vulcanized or curedto enhance their properties for use in a variety of industrial articles,such as molded or shaped parts. See for example Grootaert, W. M.,Millet, G. H. and Worm, A. T., “Fluorocarbon Elastomers”, Kirk-Othmer,Encyclopedia of Chemical Technology, Vol. 8, pp. 990-1005, 4th ed., JohnWiley & Sons, 1993. Typically they are used in the more demandingapplications where exposure to extreme heat or harsh chemical or solventenvironments is encountered.

[0004] Processes used for making molded fluoroelastomer articles, forexample O-rings, inherently have a relatively high degree of waste,e.g., 30% or higher. This waste, also commonly called scrap, may includeflash, sprue and runners, and out-of specification parts.

[0005] It is desirable to reuse (i.e., recycle) this waste material.However, for a variety of reasons, it has been very difficult to do so.For example, the waste material cannot be recycled merely by grindingand reforming as with many thermoplastic polymer operations. Usuallysuch direct addition of the waste material results in a compositionhaving a higher minimum viscosity. This increase in minimum viscositytypically negatively affects later processes, such as injection molding.

[0006] It has also been generally observed that the inclusion of wastematerial in a fluoroelastomer formulation has a negative effect on boththe cure rheology and the physical properties of articles made from suchformulations. Both are inferior to those demonstrated by formulations,and the resultant articles, that do not contain waste material (i.e.,virgin formulations and articles).

[0007] The cure rheology of a formulation containing scrap may bedeficient in several ways. For example, the cure rheology generallyexhibits a reduction in scorch time, an increase in the cure time, and alessening of final crosslink density. As a result, formulationscontaining scrap begin the onset of cure more quickly (scorch) andeither take an unacceptable amount of time to reach the desired level ofcure or crosslihk density, or fail to reach the desired cure orcrosslink density. These effects are undesirable.

[0008] The use of waste material also typically negatively affects thephysical properties of the completed articles. For example, resistanceto compression set is reduced. This is undesirable when, for example,the finished article, such as an O-ring or a gasket, will be used toform a seal. Such applications typically require a high resistance tocompression set.

SUMMARY OF THE INVENTION

[0009] The present invention relates to compositions and methods ofusing such compositions for the purpose of recycling or reusing at leastpartially vulcanized fluoroelastomers. Compositions are described whichcontain the at least partially vulcanized fluoroelastomer (a recyclecomponent) which have a cure rheology similar to that of virginfluoroelastomer compositions, i.e., compositions which contain nopreviously vulcanized fluoroelastomer. Compositions are also describedwhich contain the recycle component and which have enhanced physicalproperties.

[0010] The present invention provides, inter alia, a means of recyclingof a previously vulcanized (i.e., crosslinked) fluorinated elastomeressentially overcoming the negative effects discussed above. It providesa composition having a cure rheology similar, and in some casesvirtually identical, to that of virgin fluoroelastomer compositions.This results in a significant improvement in scorch time and crosslinkdensity as compared to previous attempts to recycle scrapfluoroelastomer. As a result, fluoroelastomer compositions of theinvention can be processed in virtually the same manner as virginfluoroelastomer compositions. Additionally, the physical properties ofthe crosslinked fluoroelastomers of the invention (e.g., tensilestrength and compression set) are noticeably enhanced. In fact, theseproperties approximate those obtained when virgin fluoroelastomer iscrosslinked.

[0011] Compositions of the present invention include (a) a mixture of acure-enhancing additive with a fluorinated elastomer gum, (b) a mixtureof the cure-enhancing additive with an at least partially vulcanizedfluorinated elastomer, and (c) a mixture of the cure-enhancing additivewith the fluorinated elastomer gum and the at least partially vulcanizedfluorinated elastomer. The present invention also includes an additivesystem useful in each of these compositions. The present inventionfurther includes the crosslinked product resulting from curing thosecompositions containing the at least partially vulcanized fluorinatedelastomer. The present invention still further includes a method ofrecycling an at least partially vulcanized fluorinated elastomer.

[0012] As used throughout this description, the following terms have thefollowing meanings:

[0013] “Fluorinated elastomer gum” and “fluoroelastomer gum” mean anessentially uncrosslinked polymer that exhibits essentially noelastomeric behavior but that can be crosslinked to provide suchbehavior. This gum is also referred to herein as being a virgin gum. Avirgin gum may also contain the ingredients of a suitably formulated andvulcanizable virgin compound.

[0014] “At least partially vulcanized fluoroelastomer” means afluoropolymer that has a measurable level of crosslinking and thatexhibits identifiable elastomeric behavior. These fluoroelastomers havebeen compounded with other materials such as crosslinking agents, acidacceptors, fillers, colorants, accelerators, process aids, etc. The atleast partially vulcanized material is also referred to herein as therecycle component.

DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows four curves that illustrate the cure rheology ofvarious fluoroelastomer materials. Curve 10 shows the cure rheology of avirgin elastomer gum. Curve 20 shows the cure rheology of a combinationof virgin fluoroelastomer gum and a recycle component. Curve 30 showsthe cure rheology of a combination of a virgin fluoroelastomer gum, arecycle component, and extra curatives. Curve 40 shows the cure rheologyof a combination of virgin elastomer gum, a recycle component, extracuratives, and cure-enhancing additives. Curves 10, 20, and 30 areexamples of the prior art. Curve 40 is an example of the presentinvention. The curves shown in FIG. 1 were generated on compositions(some of which contained a recycle component) described hereinafterusing a Monsanto Moving Die Rheometer (MDR) Model 2000 in accordancewith ASTM 5289-93A at 177° C., no preheat, 12 minute elapsed time and a0.5° arc.

DETAILED DESCRIPTION

[0016] The unique advantages of the present invention will be more fullyappreciated by reference to FIG. 1. As previously noted, curve 10 is acure rheology curve for a virgin compounded fluoroelastomer gum. Aftergoing through an initial drop in torque the composition has a relativelylong period of time at an essentially stable torque after which thetorque increases rapidly to its final or maximum value. This rapidincrease in torque is illustrated by the essentially vertical portion 11of curve 10. This rapid increase in the torque corresponds to a rapidincrease in the viscosity of the composition as it crosslinks. Therheology shown in curve 10 allows a sufficient amount of induction timefor the composition to be formed or molded before the onset of cure.This rheology also demonstrates rapid completion of the cure cycle afterthe onset of cure. As a result, the cure cycle is not unnecessarilyprolonged. Compositions which demonstrate this type of cure rheology canbe completely formed or molded rapidly, cured to a state that they canbe handled without damage, and removed from the mold for any necessarypost curing.

[0017] Curves 20 and 30 show the cure rheology of prior art attempts torecycle at least partially vulcanized fluoroelastomers. In each case,the cure rheology is significantly degraded. After the initial drop intorque, the increase in torque is not as rapid as that of virginmaterial of curve 10. This can be seen by the shallower slopes 21 and 31of curves 20 and 30. Additionally, the maximum torque is lower than thatachieved by the virgin material of curve 10. This indicates that a lowercrosslink density has been attained. As a result, such materials aremore difficult to process (e.g., use to fabricate parts) and havereduced physical properties when compared to those of either virgincompositions or those of the present invention.

[0018] Curve 40 is a cure rheology curve for a composition of theinvention. As can be seen, it closely follows cure rheology curve 10 ofthe virgin compounded fluoroelastomer gum. After the initial drop intorque, the torque increases almost as rapidly as that of the virginmaterial and significantly more rapidly than that of the prior artcompositions. Compare slope 41 with slope 11, and slope 41 with slopes21 and 31.

[0019] The maximum torque achieved with the composition of curve 40 alsoclosely approximates that of the virgin material and is substantiallyhigher than that of either of the prior art compositions exemplified bycurves 20 and 30. This indicates that compositions of the inventionattain a higher crosslink density, can be processed in virtually thesame way as virgin materials, and have physical properties that aresubstantially the same as those of virgin materials and substantiallybetter than those of the prior art compositions.

[0020] The Fluoroelastomer Gum

[0021] Fluoroelastomer gums that may be used in the present inventionare elastomeric polymers of one or more fluoromonomers selected from thegroup of vinylidene fluoride, hexafluoropropylene,chlorotrifluoroethylene, 2-chloropentafluoropropylene, perfluorinatedalkly vinyl ether, perfluorinated alkyl allyl ether,tetrafluoroethylene, 1-hydropentafluoropropylene,dichlorodifluoroethylene, trifluoroethylene, 1,1-chlorofluoroethylene,1,2-difluoroethylene, bromotrifluoroethylene, bromodifluoroethylene, andbromotetrafluorobutene. Optionally, the aforementioned one or morefluoromonomers may be copolymerized with fluorine-free olefinic monomerssuch as ethylene and propylene.

[0022] The preferred elastomer gums are copolymers of vinylidenefluoride, hexafluoropropylene, and optionally tetrafluoroethylene.Preferably these polymers comprise between about 15 and about 50 molepercent hexafluoropropylene, and up to 30 mole percenttetrafluoroethylene. Mixtures or blends of different fluorinatedelastomer gums, and fluoroelastomer gums of different viscosities ormolecular weights, are also suitable.

[0023] The fluoroelastomer gums useful in the invention may be providedas a neat gum that is free from other additives. Alternatively, they maybe provided as compounded mixtures of the gum with various otheringredients. Such ingredients include, by way of example, curatives,acid acceptors, fillers, and colorants such as dyes and pigments.

[0024] There are a number of commercially available fluoroelastomer gumsthat can be used in the invention. These include the FLUORELfluoroelastomers sold by Dyneon LLC of St. Paul, Minn. Examples of thesefluoroelastomers include the, FE, FC, FT, FG, FA and FX grades. Othercommercially available fluoroelastomer gums that may be used in theinvention include the TECHNAFLON fluoroelastomers (available fromAusimont S.p.A. of Milan, Italy), the VITON fluoroelastomers (availablefrom DuPont-Dow LLC of Wilmington, Del.) and the DLAEL fluoroelastomers(available from Daikin Industries Ltd.). Many of these gums are providedwith the curative incorporated in them.

[0025] The fluoroelastomer gum is a virgin (i.e., unvulcanized) polymerto which the recycle component is added. The exact quantity offluoroelastomer gum used in the present invention is not critical. Infact, it is not necessary to use any virgin fluoroelastomer in thepractice of the invention. When it is used, however, the virginfluoroelastomer typically comprises at least 50% by weight of the finalcomposition.

[0026] The Recycle Component

[0027] The recycle component used in the present invention compriseseither partially or completely vulcanized fluoroelastomer (hereinafter“cured fluoroelastomer”). The cured fluoroelastomer is the productobtained by crosslinking the previously described fluoroelastomer gum.

[0028] The recycle component typically comprises one or more curatives,acid acceptors, fillers and frequently process aids and colorants. Thelevel of these materials present in the recycle component is notcritical to the invention. In fact, the level varies widely.

[0029] The recycle component typically comprises flash orout-of-specification material. Flash (or runners) is the excess materialresulting from molding an article (or a string of articles). Flash isgenerally only partially vulcanized, and therefore, only partiallycrosslinked. Out-of-specification material includes parts that havesurface defects, that are not within dimensional tolerance, that are notfully formed, or that do not have the required physical properties. Theymay be either partially or completely vulcanized.

[0030] One or more cured fluoroelastomers may be used in the recyclecomponent. Additionally, the cured fluoroelastomer may have beenprepared from the same or a different gum than that used in the virginfluoroelastomer gum.

[0031] Useful primary fluoroelastomers will include the same materialslisted above as the waste product. Recycle of a similar partiallyvulcanized or fully vulcanized fluoroelastomer back into a primaryfluoroelastomer of the same type or at least one derived from the samemonomer components will likely be the most straight forward. However,materials which are not similar may also be used in the describedprocess.

[0032] The quantity of recycle component used in the present inventionis influenced by the desired processing properties and physicalproperties in the finished article. For less demanding applications,higher ratios of the recycle component are possible. This could includeusage levels as high as 100% recycle plus the cure-enhancing additivesdescribed below. For the more critical applications, such as those whichrequire a superior compression set resistance, or a maximum crosslinkdensity, recycle usage up to 50% is possible with little or nodegradation in critical physical properties.

[0033] The Additive System

[0034] The additive system used in the invention comprises acure-enhancing additive, a crosslinking agent, and an accelerator.

[0035] The Cure-enhancing Additive

[0036] The cure-enhancing additives used in the present inventionimprove the cure rheology of prior art attempts to recycle curedfluoroelastomers. This is demonstrated by the improvement in finalcrosslink density of a recycle-containing composition according to theinvention over the final crosslink density of a prior artrecycle-containing composition. Particularly preferred compositions ofthe invention also exhibit lower compression set values than do priorart recycle-containing compositions.

[0037] Examples of useful cure-enhancing additives includefluoroaliphatic sulfonamides and free radical scavengers. Combinationsof these material may be used if desired. Thus, for example, one may useone or more fluoroaliphatic sulfonamides, or one or more free radicalscavengers. Additionally, one may use one or more fluoroaliphaticsulfonamides and one or more free radical scavengers.

[0038] The fluoroaliphatic sulfonamides useful in the present inventiontypically have one or two sulfonamido groups. Useful classes of thesematerials can be represented by the general formula:

R_(f)(A)₂SO₂NR(M_({fraction (1/2)}))  I

or

R′_(f)[(A)SO₂NR(M_({fraction (1/x)})]) ₂  II

[0039] wherein

[0040] R_(f) represents a monovalent fluoroaliphatic radical having, forexample, from 1 to 20 carbon atoms, preferably 4 to 10 carbon atoms,R′_(f) represents a divalent fluoroaliphatic radical having, forexample, from 1 to 20 carbon atoms, preferably from 2 to 10 carbonatoms,

[0041] A represents an organic linkage such as —CR¹R²—, —CR¹R²CR³R⁴—,and —CR¹═CR—, wherein R¹, R², R³, and R⁴ are selected from the groupconsisting of hydrogen atom, fluorine atom, chlorine atom, and loweralkyl group, having, for example, 1 to 2 carbon atoms,

[0042] R represents hydrogen atom or alkyl radical having, for example,from 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, and

[0043] M represents hydrogen atom or salt forming cation with valence x,which is 1, 2, or 3.

[0044] The monovalent fluoroaliphatic radical, R_(f), is a fluorinated,stable, inert, non-polar, saturated moiety. It can be straight chain,branched chain, and, if sufficiently large, cyclic, or combinationsthereof, such as alkyl cycloaliphatic radicals. Generally, R_(f) willhave 1 to 20 carbon atoms, preferably 4 to 10, and will contain 40 to 83weight percent, preferably 50 to 78 weight percent fluorine.Particularly useful compounds are those in which the R_(f) group isfully or substantially completely fluorinated, as in the case whereR_(f) is perfluoroalkly, C_(n)F_(2n+1), where n is 1 to 20.

[0045] The divalent fluoroaliphatic radical, R′_(f), is a fluorinated,stable, inert, non-polar, saturated moiety. It can be straight chain,branched chain, and, if sufficiently large, cyclic, or combinationsthereof, such as alkylcycloaliphatic diradicals. Generally, R′_(f) willhave 1 to 20 carbon atoms, preferably 2 to 10. Particularly usefulcompounds are those in which the R′_(f) group is perfluoroalkyl,C_(n)F_(2n), where n is 1 to 20, or perfluorocycloalkyl, C_(n)F_(2n−2),where n is 5 to 20.

[0046] With respect to either R_(f) or R′_(f), the skeletal chain orcarbon atoms can be interrupted by divalent oxygen or trivalent nitrogenhetero atoms, each of which is bonded only to carbon atoms, butpreferably where such hetero atoms are present, such skeletal chain doesnot contain more than one said hetero atom for every two carbon atoms.An occasional carbon-bonded hydrogen atom, or chlorine atom may bepresent; where present, however, they preferably are present not morethan once for every two carbon atoms in the chain. Where R_(f) or R′_(f)is or contains a cyclic structure, such structure preferably has 5 or 6ring member atoms, 1 or 2 of which can be said hetero atoms. Examples ofR′_(f) are fluorinated alkylene, e.g., —C₄F₈—, —C₆F₁₂—. Where R_(f) isdesignated as a specific radical, e.g., C₈F₁₇—, it should be understoodthat this radical can represent an average structure of a mixture, e.g.,C₆F₁₃— to C₁₀F₂₁—, which mixture can also include branched structures.

[0047] Where R is an alkyl radical, it can be unsubstituted orsubstituted. Useful substituents include, for example, carbonyl groups,e.g.,

[0048] Fluoroaliphatic sulfonamides suitable as curing agents in thepractice of this invention include known compounds [see, for example,U.S. Pat. No. 2,732,398 (Brice et al.)]. They can be prepared by thereaction of ammonia or primary amines with perfluoroalkane sulfonylfluorides (obtained by electrochemical fluorination of alkyl or alkylenesulfonyl halides), as shown by the following reaction scheme:

R_(f)SO₂F+RNH₂→R_(f)SO₂NHR

[0049] They can also be prepared following the procedures described inU.S. Pat. No. 4,296,034 (Bouvet et al), i.e.,

R_(f)C₂H₄SO₂Cl+RNH₂→R_(f)C₂H₄SO₂NHR

[0050] Salts of the sulfonamides can be prepared by reaction of theacidic sulfonamide compound with a suitable base, as described, forexample, in U.S. Pat. No. 2,803,656 (Ahlbrecht et al):

R_(f)SO₂NHR+NaOCH₃→R_(f)SO₂N(R)⁻Na⁺

[0051] Representative fluoroaliphatic sulfonamide compounds suitable forthe practice of this invention include the following:

[0052] CF₃SO₂NH₂

[0053] CF₃SO₂N(C₄H₉)H

[0054] C₄F₉SO₂N(CH₃)H

[0055] C₈F₁₇SO₂N(CH₃)H

[0056] C₈F₁₇SO₂N(CH₃)⁻Na⁺

[0057] C₈F₁₇C₂H₄SO₂N(CH3)⁻Na⁺

[0058] HN(CH₃)SO₂(CF₂)₈SO₂N(CH₃)H

[0059] C₈F₁₇SO₂NH⁻Na⁺

[0060] C₈F₁₇SO₂N(C₁₂H₂₅)H

[0061] C₆F₁₃ SO₂N(C₂H₅)⁻K⁺

[0062] C₈F₁₇SO₂N(C₆H₅)H

[0063] C₄F₉CH₂SO₂N(CH₃)H

[0064] C₈F₁₇SO₂N(CH₃)⁻Mg⁺ _({fraction (1/2)})

[0065] C₈F₁₇C₂N(CH₃)⁻NH₄ ⁺

[0066] C₈F₁₇SO₂N(CH₃)⁻N(C₂H₅)₃H⁺

[0067] Free radical scavengers represent another class of cure-enhancingadditives usefbl in the present invention. The free radical scavengersare typically hydrogen-donating compounds. They may be used in lowconcentrations. The free radical scavengers useful in the inventioninclude those that are known and are commercially available. See forExample, “Encyclopedia of Polymer Science and Engineering,” Vol. 2, pp75-82 and 86-90, John Wiley & Sons, 1985. Representative examples ofuseful free radical scavengers include phenol compounds, phosphitecompounds, thioester compounds, and amine compounds.

[0068] Useful phenol compounds include both mono-, di-, and polyphenols.Examples of these materials are di-tertiary-butylphenol, styrenatedphenol, 2,2′-methylenebis(4-methyl-6-tert-butylphenol),4,4′-methylenebis(2,6-di-tert-butylphenol), and1,3,5-trimethyl-2,4,6-tris(3′,5′-di-tert-butyl4′-hydroxybenzyl)-benzene.

[0069] Useful phosphite compounds include tris (nonylphenyl) phosphite,distearyl pentaerythritol diphosphite, and tetrakis(2,4-di-tert-butylphenyl)4,4′-biphenylylenediphosphite.

[0070] Examples of useful thioester compounds includedistearyl-thio-propionate, didodecyl 3,3′-thiodipropionate, dimyristylthiodipropionate, and ditridecyl thiodipropionate.

[0071] Examples of useful amine compounds include one or more (andpreferably one or two) amino nitrogen atoms and at least one aryl group(or group containing one or more aryl moieties) bonded to an aminonitrogen atom. Preferably each amino nitrogen atom in the amino compoundwill be bonded to an aryl group or group containing one or more arylmoieties. However, no amino nitrogen atom in the amine compound can bedirectly bonded to the methylene carbon atom of an arylmethylene group.

[0072] Representative classes of useful amine compounds includediaryldiamines, diarylamines, diarylarylenediamines,dialkylarylenediamines, diarylalkylenediamines,tetraalkylarylenediamines, tetraarylarylenediamines, tetra(mixedalkyl/aryl) arylenediamines and tetra (mixed alkyl/aryl)alkylenediamines. Many of the amine compounds useful in this inventionare generally known and are commercially available, see for example,Nicholas P. P., Luxeder, A. M., Brooks, L. A., Hommes, P. A.,“Antioxidant and Antiozonants”, Kirk-Othmer, Encyclopedia of ChemicalTechnology, Vol. 3, pp. 128-142, 3rd ed., John Wiley & Sons, 1978.

[0073] A useful class of amine compounds can be represented by thefollowing formula:

[0074] where:

[0075] R¹ is independently selected from substituted and unsubstitutedalkly, aryl, aralkyl, and alkaryl groups;

[0076] R² is independently selected from H, and substituted andunsubstituted alkyl, aryl, aralkyl and alkaryl groups;

[0077] R³ is selected from substituted or unsubstituted arylene,alkylene, alkarylene, and aralkylene grpups;

[0078] n is a number from 0 to 3;

[0079] at least one R¹, R² or R³ group will be an aryl group or a groupcontaining one or more aryl moieties; and

[0080] no amino nitrogen atom will be bonded directly to the methylenecarbon atom of an arylmethylene (e.g., benzyl) group. Examples ofsubstituents of the R¹, R² and R³ groups include halogen atoms, alkyl(e.g., methyl, octyl, and t-butyl), alkoxy, alkylthio and aryl groups.

[0081] Examples of particularly useful amine compounds areN,N-′di-beta-naphthyl-para-phenylene diamine (i.e.,C₁₀H₇—NH—C₆H₄—NH—C₁₀H₇, formerly commercially available as “AGERITEWHIT”, C₆H₅ —NH—C₆H₄—NH—C₆H₅, available commercially as “AGERITE DPPD”,both compounds available from R. T. Vanderbilt Company, Inc.,C₆H₅—NH—C₆H₅ and

[0082] para, Cl—C₆H₄—N(C₆—H₅)—C₆H₄—N(C₆H₅)—C₆H₄—Cl para.

[0083] The following table lists a number of commercially availableamine compounds, including the AGERITE™ materials, that are useful inthe invention. Amine Structure MW Source Product NameC₁₀H₇—NH—C₆H₄—NH—C₁₀H₇ 360 Vanderbilt AGERITE WHITE C₆H₅—NH—C₆H₄—NH—C₆H₅260 Vanderbilt AGERITE DPPD CH₃(CH₂)₆NH—C₆H₄—NH(CH₂)₆CH₃ 304 Pfaltz &026430 Bauer C₆H₅—NH—CH₂CH₂—NH—C₆H₅ 212 Aldrich D2700-4 [paraCl—C₆H₄—N(C₆H₅)]₂—C₆H₄ 481 TCI B1336 (CH₃)₂N—C₆H₄—N(CH₃)₂ 164 Aldrich16020-2 4-phenylpiperidine 161 Aldrich 14861-1 C₆H₅—NH—C₆H₅ 169 FisherD-91

346 Naugatuck Dibenzo GMF

[0084] Any cure-enhancing additive may be used by itself Alternatively,any combination of the cure-enhancing additives may be used in theinvention.

[0085] An effective amount of cure-enhancing additive is used in theinvention. An effective amount is that which improves the maximum torqueattained over that attained using a comparable composition that does notcontain the cure-enhancing additive. The precise amount ofcure-enhancing additive employed is influenced by a number of factorsincluding the molecular weight of the particular additive molecule, thedegree to which the recycle component has been crosslinked, and theamount of recycle component being added. Generally, the cure-enhancingadditive is present in amounts ranging from 1 to 1000 millimoles per 100parts (mmhr) of the recycle component composition employed. Preferably,the cure-enhancing additive is present in amounts ranging from 1 to 50mmhr, and more preferably in amounts ranging from 1 to 25 mmhr.

[0086] The Crosslinking Agent

[0087] Crosslinking agents useful in the additive system are thoseuseful for curing vinylidene fluoride-containing polymers. Thesecrosslinking agents, also known as curing agents, include both theconventional curing agents used to cure fluoroelastomers, i.e., organicand inorganic peroxides, polyhydroxy compounds or derivatives thereoforganic polyamines or derivatives thereof, and fluoroaliphatic polyolsand allyl ethers and carbonates of aromatic polyhydroxy compounds.

[0088] The polyhydroxy compounds and their derivatives represent apreferred class of curatives. The compounds are well known and aredescribed in the art in U.S. Pat. Nos. 4,259,463; 3,876,654; 4,233,421and 5,262,490. Polyhydroxy compounds useful in the invention are alsodescribed in U.S. Pat. Nos. 3,655,727; 3,721,877; 3,857,807; 3,686,143;3,933,372; and 4,358,559. The disclosures of these references withregard to these compounds is incorporated herein by reference. Thesecompounds can be either aromatic or aliphatic polyhydroxy compounds ortheir derivatives. Blends of such compounds may be used if desired.

[0089] Representative examples of useful crosslinking agents are:

[0090] Hydroquinone, resorcinol

[0091] 4,4′-dihydroxydiphenylsulfone (Bisphenol S)

[0092] 2,4′-dihydroxydiphenylsulfone

[0093] 2,2-isopropylidine-bis(4-hydroxybenzene) (Bisphenol A)

[0094] 2,2-hexafluoroisopropylidine-bis (4-hydroxybenzene) (BisphenolAF)

[0095] 4,4′-dihydroxybenzopheonone 4,4′-biphenol

[0096] 1-allyloxy4-hydroxybenzene

[0097] Bisphenol A monoallyl ether

[0098] Dicarbonate blocked Bisphenol AF compounds

[0099] 1,4-bis(hydroxymethyl) perfluorobutane

[0100] Hexamethylenediarnine carbamate

[0101] N,N′-dicinnamylidene-1,6-hexanediamine.

[0102] Mixtures of the foregoing can also be used.

[0103] The Accelerator

[0104] Accelerators useful in the invention are organo-onium compounds.These compounds accelerate the cure of the composition of the invention.

[0105] The organo-onium compounds are phosphonium, ammonium, orsulfonium compounds which are conjugate acids of a phosphine, amine, orsulfide. They can be formed by reacting said phosphine, amine, orsulfide with a suitable alkylating agent (e.g., an alkyl halide or acylhalide) resulting in the expansion of the valence of the electrondonating phosphorous, nitrogen, or sulfur atom and a positive charge onthe organo-onium compound. The organo-onium compounds suitable for usein this invention are known and are described in the art. See, forexample, U.S. Pat. No. 4,882,390 (Grootaert et al.), U.S. Pat. No.4,233,421 (Worm), U.S. Pat. No. 5,086,123 (Guenthner et al.), and U.S.Pat. No. 5,262,490 (Kolb et al.) which descriptions are incorporated byreference.

[0106] Said phosphonium compounds include those selected from the groupconsisting of amino-phosphonium, phosphorane (e.g., triarylphosphorane),and phosphorous containing iminium compounds.

[0107] One class of phosphonium or ammonium compounds broadly comprisesrelatively positive and relatively negative ions (the phosphorous ornitrogen atom generally comprising the central atom of the positiveion), these compounds being generally known as ammonium or phosphoniumsalts or compounds.

[0108] Another class of phosphonium compounds useful in this inventionare amino-phosphonium compounds some of which are described in the art,see for example, U.S. Pat. No. 4,259,463 (Moggi et al.).

[0109] Another class of phosphonium compounds useful in this inventionare phosphorane compounds such as triarylphosphorane compounds; some ofthe latter compounds are known and are described in the art, see forexample, U.S. Pat. No. 3,752,787 (de Brunner), which descriptions areherein incorporated by reference.

[0110] Another class of iminium compounds useful in this invention aredescribed in the art, e.g., European Patent Applications 182299A2 and120462A1 which descriptions are herein incorporated by reference.

[0111] Representative phosphonium compounds includetetramethylphosphonium chloride, tetrabutylphosphonium chloride,tributylbenzyl phosphonium chloride, tributylallylphosphonium chloride,tetraphenylphosphonium chloride, benzyltris(dimethylamino)phosphoniumchloride, bis(benzyldiphenylphosphine)iminium chloride, andtriphenylbenzylphosphonium chloride.

[0112] Sulfonium compounds useful in this invention are known anddescribed in the art, e.g., see U.S. Pat. No. 4,233,421 (Worm). Brieflydescribed, a sulfonium compound is a sulfur-containig organic compoundin which at least one sulfur atom is covalently bonded to three organicmoieties having from 1 to 20 carbon atoms by means of carbon-sulfurcovalent bonds and is ionically associated with an anion. Said organicmoieties can be the same or different. The sulfonium compounds may havemore than one relatively positive sulfur atom, e.g.,[(C₆H₅)₂S⁺C₆H₄S⁺(C₆H₅)₂]2Cl⁻, and two of the carbon-sulfur covalentbonds may be between the carbon atoms of a divalent organic moiety,i.e., the sulfur atom may be a heteroatom in a cyclic structure.

[0113] The relative quantities of the cure-enhancing additive, thecrosslinking agent and the accelerator used in the additive system areinfluenced by the amount of recycle component being employed, the degreeto which the recycle component has been crosslinked, and the level ortype of improvement desired in the finished product. The precise levelof the additive system employed is that which is effective in improvingthe cure rheology of the composition of the invention as compared withthat of a similar composition that does not employ the additive system.

[0114] Typically, the additive system will comprise from about

[0115] (a) 1 to 45 weight percent of the cure-enhancing agent,

[0116] (b) 1 to 75 weight percent of the crosslinking agent, and

[0117] (c) 1 to 40 weight percent of the accelerator.

[0118] Generally, the additive system comprises from about

[0119] (a) 1 to 30 (preferably 10 to 25) weight percent of thefluoroaliphatic sulfonamide and 1 to 15 (preferably 5 to 15) weightpercent of the free radical scavenger,

[0120] (b) 1 to 65 (preferably 35 to 50) weight percent of thecrosslinking agent, and

[0121] (c) 1 to 35 (preferably 10 to 25) weight percent of theaccelerator.

[0122] The quantity of the additive system used in the invention is alsothat which is effective to improve the cure rheology of a composition ofthe invention as compared to a similar composition that does not employthe additive system. Generally, this level of the additive system usedwill be that which provides the previously discussed quantities ofcure-enhancing additives to the final composition.

[0123] Other Adjuvants

[0124] A variety of other adjuvants may be employed in the compositionsof the invention. Such materials include acid acceptors, colorants,processing aids, and reinforcing fillers.

[0125] Useful acid acceptors can be inorganic or organic compounds.Organic acid acceptors include sodium stearate and magnesium oxalate.However, acid acceptors are generally inorganic bases and includemagnesium oxide, lead oxide, calcium oxide, calcium hydroxide, dibasiclead phosphite, zinc oxide, barium carbonate, strontium hydroxide,calcium carbonate, etc. The preferred acid acceptors are magnesium oxideand calcium hydroxide. The acid acceptors can be used singly or incombination and typically are used in amounts ranging from 2 to 25 partsper 100 parts by weight of the virgin gum.

[0126] Colorants useful in the invention are dyes or pigments. The mostcommon pigment is carbon black.

[0127] Processing aids useful in the invention may include carnauba wax,aliphatic esters, carboxylic acids, and diorgano sulfur oxides such asdichlorodiphenylsulfone.

[0128] The cured fluoroelastomer may be recycled according to theinvention by preferably reducing the recycle component to a sizesuitable for easy handling, refining the cured fluoroelastomer, blendingthe additive system with the cured fluoroelastomer and crosslinking theresulting blend.

[0129] The size of the cured fluoroelastomer can be reduced by grindingor comminuting using the methods described in U.S. Pat. Nos. 4,535,941;4,625,922; and 5,411,215.

[0130] The cured fluoroelastomer can be refined by mixing it in aninternal mixer, or miling it on a two-roll mill. Both types of devicesare well known in the art. The two-roll mills have the ability toprocess materials at a small nip (that is a narrow gap between therolls).

[0131] Refining assists in recycling the cured fluoroelastomer bybreaking the crosslinks present and reducing the molecular weight of thecured fluoroelastomer. Refining can be carried out with or without theadditive system being present. Preferably the cured fluoroelastomer isrefined until a continuous mass is obtained, after which the additivesystem is blended into the mass.

[0132] A particularly useful means of recycling the curedfluoroelastomer employs a carrier gum in combination with the recyclecomponent and the additive system. The carrier gum may be any uncuredfluoroelastomer that is compatible with the final composition. Examplesof such carrier gums include the uncured fluoroelastomers describedpreviously as fluoroelastomer gums. The carrier gum is employed tofacilitate the incorporation of the additive system. Typically, theadditive system is blended into the carrier gum. This blend may then becombined with the recycle component on, for example, a conventionaltwo-roll mill, a refining mill, or an internal mixer to blend in therecycle component. The type of mixing device used will depend on theamount and form of recycle component to be used. The carrier gum isusually present as a minority component. The exact amount used will bevaried depending on the crosslink density of the cured fluoroelastomer,the amount of recycle component desired in the final composition, etc. Atypical range of carrier gum to recycle component is 0 to 100 parts ofcarrier gum to 100 parts of recycle component. A preferred range foroptimum property enhancement is 10 to 30 parts carrier gum to 100 partsrecycle component. However, more or less carrier gum may be used ifdesired.

[0133] The blend of recycle component, additive system, and optionalcarrier gum may be used by itself if desired. Alternatively it may becombined with the virgin fluoroelastomer gum to form the finalcomposition. In either case, the other adjuvants are typically added atthis time. In the latter case, the various components, including theother adjuvants, may be combined on a two-roll mill or in an internalmixing device using techniques known in the art.

[0134] The techniques used for refining and final blending are somewhatdissimilar. For example, when a two-roll mill is employed the ratio ofroll speeds is typically in the range of 1:1 or higher. Ratios of 1.4:1to 2.0:1 are preferred for the refining step. Lower ratios, e.g., 1.1 to1.4 can be used. But residence time may need to be increased. A tightmill roll gap or nip is beneficial in providing sufficient shear rate inthe vicinity of 200-1000 sec⁻¹ or preferably 300-700 sec-⁻¹ for suitableresidence or processing time.

[0135] Final blending is typically done at a wider nip setting or lessroll speed differential resulting in more conventional shear rates of50-200 sec⁻¹ typically 100-150 sec⁻¹.

[0136] The exact ratio of roll speeds in refining and final blending isdetermined by the result desired in the finished product.

[0137] For best results the temperature of the mixture on the mixingdevice should not rise above about 120° C. During mixing it is necessaryto distribute the components and adjuvants uniformly throughout thecomposition.

[0138] The curing process typically comprises extrusion or pressing thefinal composition in a mold, e.g., a cavity or a transfer mold, andsubsequently oven curing. The composition of this invention isparticularly useful for injection molding. Pressing of the compoundedmixture (press cure) is typically conducted at a temperature betweenabout 95° C. and about 230° C., preferably between about 150° C. andabout 205° C. for a period of from 1 minute to about 15 hours, usuallyfrom 5 minutes to 30 minutes. A pressure of between about 700 kPa andabout 20,600 kPa, preferably between about 3,400 kPa and about 6,800 kPais imposed on the compounded mixture in the mold. The molded vulcanizateis then usually post cured (oven cured) at a temperature between about150° C. and about 315° C., usually at about 232° C. for a period of fromabout 2 hours to 50 hours or more depending on the cross-sectionalthickness of the sample. For thick sections, the temperature during thepost cure is usually raised gradually from the lower limit of the rangeto the desired maximum temperature selected. For thinner cross-sections,e.g., less than 5 mm, the vulcanizate or cured sheet section may be putinto the oven at the desired maximum temperature. The maximumtemperature used is preferably about 260° C. and is held at this valuefor about 4 hours or more.

[0139] One major utility of the vulcanized compositions of thisinvention lies in their use as shaft seals in automotive applications,gaskets, O-rings and the like, for containing fluids under pressure atelevated temperatures, as, for example, in hydraulic systems inaircraft, or as components of reactors and fluid transfer lines used inthe processing of chemicals.

[0140] The following examples are offered to aid in a betterunderstanding of the present invention and are not to be unnecessarilyconstrued as limiting the scope thereof

EXAMPLES

[0141] In the following examples, quantities of at least partiallyvulcanized fluoroelastomers are incorporated into compositions of theinvention and cured and tested. The compounding was done on aconventional two-roll mill (13 in×6 in/32.5 cm×15 cm) with a 1.4 to 1ratio and a surface speed on the slow roll of 7.6 in/sec (19.1 cm/sec).Testing was done using the following test methods.

[0142] Test Methods

[0143] Mooney viscosity was determined by ASTM 1646-94 (MS 121° C.).Results are reported in Mooney units.

[0144] Cure Rheology Tests were run on compounded admixtures using aMonsanto Moving Die Rheometer (MDR) Model 2000 in accordance with ASTM D5289-93a at 177° C., no preheat, 12 minute elapsed time (unlessotherwise specified) and a 0.5° arc. Minimum torque (M_(L)), Maximumtorque (M_(H)), i.e., highest torque attained during specified period oftime when no plateau or maximum was obtained. Also reported were: t_(s)2(time for torque to increase 2 units above M_(L)), t′50 (time for torqueto reach M_(L)+0.5[M_(H)−M_(L)]), and t′90 (time for torque to reachM_(L)+0.9[M_(H)−M_(L)]).

[0145] Press-ured samples (150×150×2.0 mm sheets, unless otherwisenoted) were prepared for physical property determination by pressing atabout 6.9 MegaPascals (MPA) for the indicated amount of time andtemperature.

[0146] Post-cured samples were prepared by placing a press-cured samplein a circulating air oven. The oven was maintained at 232° C. and thesamples treated for 16 hours (unless otherwise noted).

[0147] Compression set determined by ASTM D 395-89 Method B with 0.139inch (3.5 mm) 0-rings compressed for 70 hours at 200° C. Results arereported as %. MATERIAL GLOSSARY The following materials were used inthe Examples: Fluorel ™ Unvulcanized dipolymer fluoroelastomer gumFluoroelastomer containing incorporated curatives, (typical fluorineFE-5620Q content of 65.9%, approximate Mooney viscosity of 23) availablefrom Dyneon LLC, St. Paul, Minnesota Fluorel ™ Unvulcanized dipolymerfluoroelastomer gum Fluoroelastomer containing incorporated curatives,(typical fluorine FC-2179 content of 65.9%, approximate Mooney viscosityof 80 at 121° C.) available from Dyneon LLC, St. Paul, MinnesotaCopolymer A Copolymer of 78 mole % vinylidene difluoride (VF₂) and 22mole % hexafluoropropylene (HFP), (approximate Mooney viscosity of 75 at121° C.) Copolymer B Copolymer of 78 mole % VF₂ and 22 mole % HFP(approximate Mooney viscosity of 20 at 121° C.) Carbon Black N-990available from J.P. Huber Corp. of Borger, Texas Ca(OH)2 HP Gradeavailable from C.P. Hall MgO Elastomag ™ 170 available from Morton ofManistee, Michigan Bisphenol AF HOØ-C(CF₃)₂-Ø-OH available from AldrichChemical Co. Accelerator A Reaction product of equimolar quantities oftriphenyl benzyl phosphonium chloride (available from Aldrich ChemicalCo.) and the sodium salt of Bisphenol AF as described in U.S. Pat. No.5,262,490. Accelerator B Reaction product of equimolar quantities oftriarylsulfonium chloride (available from Auto Corporation) and thesodium salt of Bisphenol AF as described in U.S. Pat. No. 5,262,490.dtbP Di-tertiary butyl phenol available from Aldrich Chemical Co. DBSDibutyl sebacate available from Harwick Chemical Co. DPPD AGERITE DPPD(C₆H₅—NH—C₆H₄—NH—C₆H₅) available from R.T. Vanderbilt Company, Inc.DBS/DPPD 50/50 blend of DBS and AGERITE DPPD Irganox Irganox 1520, aphenol-containing free radical scavenger available from Ciba GeigyIrgafos Irgafos 168, a phosphite-containing free radical scavengeravailable from Ciba Geigy DSTDP Distearyl-thio-dipropionate free radicalscavenger available from Cytec CF-120 Tocopherol, a free radicalscavenger available from Rhonotec

Examples 1-9

[0148] The following examples of the invention were prepared by making arecycle component and a carrier gum. The recycle component, the carriergum, an additive system and a fluoroelastomer gum were then combined,press-cured and tested. The compositions employed and the resultsobtained are set out in Table 1.

[0149] A partially vulcanized fluoroelastomer (the recycle component)was prepared from the following formulation: Component Parts by WeightFE-5620Q 100 N-990 30 Ca(OH)₂ 6 MgO 3

[0150] The components were combined together on a conventional two-rollmill until a uniform blend was obtained. The blend was removed from themill pressed into sheets about 2 mm thick and partially cured (i.e.,press-cured). Pressing and partially curing took place at 177° C. for 12minutes. The resulting sheets of recycle component were cut into smallpieces (i.e., about 12 cm square) for future use.

[0151] A carrier gum was made on a conventional two-roll mill bycombining the following components: Component Parts by Weight CopolymerA 50 Copolymer B 50 Bisphenol AF 5.96 Accelerator A 1.97 Accelerator B2.78 C₈F₁₇SO₂NHCH₃ 4.17 Free Radical Scavenger 2.08

[0152] The carrier gum components were combined together on the mill andblended until a uniform mixture was obtained. The resulting carrier gumwas then removed from the mill in an uncured state.

[0153] The nip of the mill was then tightened to 0.006 inches (0.15 mm).This represented a shear rate of about 500 sec⁻¹. Full cooling wasapplied to the mill. Twenty-five grams of the carrier gum were added tothe nip. Then, 75 g of the recycle component were slowly added to thenip. The recycle component first formed a crumbled powder, and thenformed a compound that banded on the mill and could be worked into thecarrier gum. The resulting carrier/recycle blend was removed from themill.

[0154] The final composition was made by blending 84 g of FE-5620Q, 27.9g carbon black, 5.6 g Ca(OH)₂ and 2.8 g MgO on the two roll mill. Tothis was added 41.7 g of the carrier/recycle blend.

[0155] The resulting composition had an overall loading offluoroelastomer gum as follows:

[0156] 70 parts FE-5620Q

[0157] 7.5 parts of the Copolymer A and Copolymer B component of thecarrier gum composition

[0158] 22.5 parts of the FE-5620Q from the recycle component.

[0159] 100 parts total

[0160] The above composition was then filled to an overall loading of 30phr (parts per hundred of rubber or gum) of N-990 carbon black, 6 phr ofCa(OH)₂ and 3 phr of MgO. Because the recycle component alreadycontained 30 phr carbon black, 6 phr Ca(OH)₂ and 3 phr MgO, the actualquantities of these materials added to the mill were adjustedaccordingly to give the final overall composition.

[0161] The finished product contained virgin fluoroelastomer gumcomposition, carrier gum, recycle component, extra curatives for therecycle component and cure-enhancing additives. Rheology (cure curve)testing was performed on the finished composition before anypress-curing was done. The finished composition was then press-curedinto a sheet for 12 minutes at 177° C. and post-cured for 16 hours at232° C. Physical properties were tested on post-cured sheets.Compression set results were obtained after a 70 hours test at 200° C.The results are listed in Table 1.

Comparative Example C1

[0162] This example consisted of the following virgin fluoroelastomergum composition: FE-5620Q 100 g Carbon Black  30 g Ca(OH)₂  6 g MgO  3 g

[0163] The ingredients were combined on a two-roll mill until a uniformblend was obtained. The blend was removed from the mill, pressed intosheets about 2 mm thick. The finished product contained no carrier gumand no recycle component, extra curative, or cure-enhancing additives.Rheology testing and physical property testing was done as in Examples1-9. The results are listed in Table 1.

Comparative Example C2

[0164] This comparative example was prepared and tested as described inExamples 1-9 except that the carrier gum employed comprised onlyCopolymer A and Copolymer B. This composition included virginfluoroelastomer gum, partially vulcanized recycle component and carriergum but no extra curative, no cure accelerator or cure-enhancingadditives. The results of the tests are listed in Table 1.

Comparative Example C3

[0165] This example was prepared and tested as in Examples 1-9 exceptthat the carrier gum employed no C₈F₁₇SO₂NHCH₃ and no free radicalscavengers. This composition included virgin fluoroelastomer gumcomposition, carrier gum, recycle component, extra curative, but nocure-enhancing additives. The test results are listed in Table 1.

[0166] The cure rheology curves of Comparative Examples C1, C2, C3, andExample 9 are illustrated as curves 10, 20, 30 and 40 respectively inFIG. 1. TABLE 1 Cure-Enhancing Additive Recycle Carrier Free RadicalM_(L) M_(H) t_(S)2 t′50 t′90 Compression Ex. Component Gum C₈F₁₇SO₂NHCH₃Scavenger (dN-m) (dN-m) (min) (min) (min) Set % C1 No No No No 0.9 30.23.4 3.4 5.1 17.3 C2 Yes Yes No No 1.7 13.9 2.5 3.1 5.4 25.6 C3 Yes YesNo No 1.6 21.8 2.1 3.8 6.2 23.1 1 Yes Yes Yes No 1.6 26.2 2.5 3.8 5.921.9 2 Yes Yes Yes dtbP 1.5 25.4 2.4 3.6 5.8 18.8 3 Yes Yes Yes Irganox1.5 26.7 2.3 3.4 5.6 26.9 4 Yes Yes Yes Irgafos 1.5 25.2 2.3 3.4 5.520.8 5 Yes Yes Yes DPPD 1.6 26.0 2.4 3.7 5.9 21.0 6 Yes Yes Yes DBS 1.527.7 2.4 3.4 5.5 20.1 7 Yes Yes Yes DSTDP 1.6 27.9 2.4 3.5 5.6 20.8 8Yes Yes Yes CF-120 1.7 24.7 1.8 2.6 4.3 24.7 9 Yes Yes Yes DBS/DPPD 1.627.2 2.5 3.4 5.2 19.6

[0167] The data in Table 1 show that Comparative Example C1, virginfluoroelastomer gum composition (i.e., one free of a recycle component),has the highest final crosslink density (as shown by the highest M_(H))and the best compression set (i.e., the lowest compression set value).It also shows that this composition reaches its maximum crosslinkdensity very rapidly.

[0168] By way of contrast, Comparative Example C2 shows thatincorporating a recycle component into the virgin fluoroelastomerwithout adding extra curatives significantly reduces the final crosslinkdensity and negatively affects its compression set. The reduction incompression set is shown by the increase in the compression set value.

[0169] Comparative Example C3 shows that the addition of extra curativesto a composition like that of Comparative Example C2 improves the finalcrosslink density. However, the final crosslink density is still wellbelow that of the virgin material. Further, the compression set is stillnegatively affected as shown by the high compression set value whencompared to that of virgin material.

[0170] Examples 1-9 each show that when the cure-enhancing additives areused, the final crosslink density of the cured composition issignificantly better than that achieved by merely adding recyclecomponent as was done in Comparative Examples C2 or the recyclecomponent plus additional curatives as was done in Comparative ExampleC3. The data further shows that final crosslink density approximatesthat of the virgin gum composition.

Examples 10-12

[0171] Fluoroelastomer gum and recycle component were prepared asdescribed in Examples 1-9. One hundred grams of the recycle componentwere refined on a two-roll mill having a nip setting of 0.15 mm(corresponding to a shear of about 500 reciprocal seconds). Full coolingwas applied to the mill. No carrier gum was used. The recycle componentfirst formed a crumbled powder and then banded to the mill and could beworked. Extra curatives (1.02 g of Viton™ Cure 50 curative, a mixture ofBisphenol AF and phosphonium curatives available from DuPont-Dow LLC,and 0.32 g of Bisphenol AF), 4.17 g of C₈F₁₇SO₂NHCH₃ and 2.08 g of freeradical scavenger were added to the recycle component and blended intoit. The free radical scavenger was used in Examples 11 and 12 only. Then345 g of the compounded virgin fluoroelastomer gum of ComparativeExample C1 was added to the blend of recycle component, extra curatives,and cure-enhancing additives. This composition was milled until auniform blend was achieved. The final composition included virginfluorinated elastomer gum composition, partially vulcanized recyclecomponent, extra curatives and cure-enhancing additives. Thecompositions were cured and tested as described in Example 1. Theresults obtained are shown in Table 2.

Comparative Example C4

[0172] This example was prepared and tested as described in Examples10-12 except that no extra curative and no cure-enhancing additives wereused. The final composition consisted of virgin fluoroelastomer gum, therecycle component but no carrier gum, extra curatives or cure-enhancingadditives. The test results are shown in Table 2.

Comparative Example C5

[0173] This example was prepared and tested as described in Examples10-12 except that no cure-enhancing additives were used. The finalcomposition consisted of the virgin fluoroelastomer gum and the recyclecomponent and extra curatives. It employed no carrier gum orcure-enhancing additives. Test results obtained are shown in Table 2.TABLE 2 Cure-Enhancing Additive Recycle Carrier Free Radical M_(L) M_(H)t_(S)2 t′50 t′90 Compression Ex. Component Gum C₈F₁₇SO₂NHCH₃ Scavenger(dN-m) (dN-m) (min) (min) (min) Set (%) C1 No No No No 0.9 30.2 3.4 3.45.1 17.3 C4 Yes No No No 1.6 12.3 2.1 3.2 6.1 27.2 C5 Yes No No No 1.820.7 1.6 3.9 4.7 20.9 10 Yes No Yes No 1.9 23.7 1.8 2.9 5.3 20.4 11 YesNo Yes dtbP 1.7 24.4 1.7 2.6 4.3 18.5 12 Yes No Yes DBS 1.7 24.6 1.8 2.43.9 18.7

[0174] The data in Table 2 show that the carrier gum is not essential tothe present invention. The data further shows that the present inventionprovides improved final crosslink density over that obtained with priorattempts to incorporate recycle fluoroelastomer. Finally, the data showthat the present invention provides improved compression set.

Examples 13-16

[0175] These examples were prepared and tested as described in Examples1-9 except that Fluorel FC-2179 fluoroelastomer gum was substituted forFluorel FE-5620Q in making the recycle component and in the virginfluoroelastomer gum. Additionally, no extra curatives and no carrier gumwas used. Further, the level of cure-enhancing additive used wassufficient to provide 0.8 parts of C₈F₁₇SO₂NHCH₃ per hundred parts oftotal fluoroelastomer gum, or 0.4 parts of free radical scavenger perhundred parts of fluoroelastomer gum. The final composition comprisedvirgin fluoroelastomer gum composition, press-cured (i.e., partiallyvulcanized) recycle component, carrier gum and cure enhancing agents.The test results are shown in Table 3.

Examples 17-18

[0176] These examples were prepared and tested as described in Examples13-16 except that the recycle component was both press-cured andpost-cured (i.e., it was essentially completely vulcanized) before beingincorporated into the final composition. The results of the physicaltests are given in Table 3.

Comparative Example C6

[0177] This example was prepared and tested as described in Examples C1except that the virgin fluoroelastomer gum composition used FC-2179instead of FE-5620Q. The results of the physical tests are given inTable 3.

Comparative Example C7

[0178] This example was prepared and tested as described in Examples13-16 except that although the recycle component was used, no extracurative or cure-enhancing agents were employed. The results of thephysical tests are given in Table 3.

Comparative Example C8

[0179] Comparative Example C7 was repeated except that the recyclecomponent was essentially completely vulcanized before beingincorporated into the final composition. The results of the physicaltests are given in Table 3. TABLE 3 Cure-Enhancing Additive RecycleCarrier Free Radical M_(L) M_(H) t_(S)2 t′50 t′90 Compression Ex.Component Gum C₈F₁₇SO₂NHCH₃ Scavenger (dN-m) (dN-m) (min) (min) (min)Set (%) C6 No No No No 4.3 33.2 1.3 2.4 3.3 10.5 C7 Yes No No No 6.217.6 1.0 2.0 5.5 34.4 C8 Yes No No No 6.4 12.9 1.8 3.0 9.5 41.7 13 YesNo No DBS 6.1 19.4 0.8 1.4 3.1 31.1 14 Yes No No dtbP 6.2 19.4 0.8 1.43.0 29.1 15 Yes No No DPPD 6.2 19.1 0.8 1.7 3.9 32.3 16 Yes No Yes No6.2 20.3 1.0 2.3 4.9 25.3 17 Yes No No dtbP 6.2 16.7 1.2 3.5 9.4 34.6 18Yes No Yes No 6.1 14.1 1.5 3.9 10.2 31.0

[0180] The data in Table 3 demonstrate that incorporating a recyclecomponent into virgin fluoroelastomer gum, even with extra curativesbeing present, substantially lowers the final crosslink density. It alsosubstantially reduces the compression set resistance of the composition.Compare the M_(H) and Compression Set values of Comparative Example C6(virgin material) with those of Comparative Example C7.

[0181] The data further show that incorporating a cure-enhancing agentinto the composition substantially improves MH and generally improvesresistance to compression set over Comparative Example C7.

[0182] The data in Table 3 show improvement in both final crosslinkdensity and resistance to compression set when the cure-enhancing agentsare used to recycle at least partially vulcanized fluoroelastomer.

[0183] Finally, the data demonstrates that the benefits of the presentinvention are achieved even when essentially fully vulcanized recyclecomponent is used.

Examples 19-21

[0184] Examples 19-21 were prepared and tested as described in Examples1-9 except that the amount of the carrier/recycle blend combined withthe virgin fluoroelastomer gum was adjusted so that the recyclecomponent comprised 10%, 20% or 30% of the total composition.Additionally, the carrier gum contained dichlorodiphenylsulfone (DCDPS)in an amount sufficient to provide 0.9 parts of DCDPS per 100 parts offluoroelastomer gum. The test results are listed in Table 4. TABLE 4Cure-enhancing Additive Recycle Carrier Free Radical M_(L) M_(H) t_(S)2t′50 t′90 Compression Ex. Component Gum C₈F₁₇SO₂NHCH₃ Scavenger (dN-m)(dN-m) (min) (min) (min) Set (%) C1 No No No No 0.9 30.2 3.4 3.4 5.117.3 C2 Yes Yes No No 1.7 13.9 2.5 3.1 5.4 25.6 (22.5%) C3 Yes Yes No No1.6 21.8 2.1 3.8 6.2 23.1 (22.5%) 19 Yes Yes Yes DBS/DPPD 1.2 27.0 2.93.9 6.3 16.2 (10%) 20 Yes Yes Yes DBS/DPPD 1.7 26.7 2.6 3.9 5.9 19.9(20%) 21 Yes Yes Yes DBS/DPPD 2.4 27.4 2.0 3.4 5.9 21.9 (30%)

[0185] The foregoing detailed description and examples have been givenfor clarity of understanding only. No unnecessary limitations are to beunderstood therefrom. The invention is not limited to the exact detailsshown and described, for variations obvious to one skilled in the artwill be included within the invention defined by the claims.

1. An additive system used to recycle at least partially vulcanizedfluorinated elastomer comprising an effective amount of each of thefollowing: (a) a cure-enhancing additive; (b) a crosslinking agent; and(c) an accelerator.
 2. An additive system according to claim 1 whereinthe cure-enhancing additive comprises at least one material selectedfrom the group consisting of a free radical scavenger, a fluoroaliphaticsulfonamide, and a mixture of such materials.
 3. An additive systemaccording to claim 2 wherein the crosslinking agent is selected from thegroup consisting of an aromatic polyhydroxy-containing compound.
 4. Anadditive system according to claim 3 wherein the accelerator comprisesan organo-onium compound.
 5. An additive system according to claim 1comprising (a) from 1 to 45 percent by weight of the cure-enhancingadditive; (b) from 1 to 75 weight percent of the crosslinking agent; and(c) from about 1 to 40 weight percent of the accelerator.
 6. An additivesystem according to claim 5 wherein (a) the cure-enhancing additivecomprises a fluoroaliphatic sulfonamide and a free radical scavenger;(b) the crosslinking agent is selected from the group consisting oforganic peroxides, inorganic peroxides, polyhydroxides and derivativesthereof, organic polyamines and derivatives thereof, fluoroaliphaticpolyols, allyl ethers of polyhydroxy compounds, and allyl carbonates ofpolyhydroxy compounds; and (c) the accelerator comprises an organo-oniumcompound.
 7. An additive system according to claim 1 further comprisinga processing aid.
 8. A composition comprising: (a) at least onefluoropolymer selected from the groups consisting of (i) an unvulcanizedfluorinated elastomer gum, and (ii) an at least partially vulcanizedfluorinated elastomer, and (b) an effective amount of a cure-enhancingadditive.
 9. The composition according to claim 8 wherein thefluoropolymer comprises the at least partially vulcanized elastomer. 10.The composition according to claim 8 wherein the fluoropolymer comprisesthe unvulcanized fluorinated elastomer gum.
 11. The compositionaccording to claim 8 further comprising: (c) an effective amount of atleast one crosslinking agent.
 12. The composition of claim 11 furthercomprising (d) an effective amount of an accelerator.
 13. Thecomposition according to claim 8 further comprising a processing aid.14. The composition according to claim 8 wherein (a) the cure-enhancingadditive comprises a fluoroaliphatic sulfonamide and a free radicalscavenger; (b) the crosslinking agent is selected from the groupconsisting of organic peroxides, inorganic peroxides, polyhydroxides andderivatives thereof, organic polyamines and derivatives thereoffluoroaliphatic polyols, allyl ethers of polyhydroxy compounds, andallyl carbonates of polyhydroxy compounds; and (c) the acceleratorcomprises an organo-onium compound.
 15. The composition according toclaim 13 wherein the cure-enhancing additive is a free radical scavengerselected from the group consisting of phenol compounds, phosphitecompounds, thioester compounds, and amine compounds.
 16. The compositionaccording to claim 14 wherein the cur nhancing agent comprises a mixtureof the free radical scavenger and the fluoroaliphatic sulfonamide.
 17. Acomposition useful to recycle cured fluoroelastomer materialscomprising: (a) a recycle component comprising an at least partiallyvulcanized fluoroelastomer, (b) an effective amount of an additivesystem comprising (i) a cure-enhancing additive selected from the groupconsisting of fluoroaliphatic sulfonamide, a free radical scavenger, anda mixture of the two, (ii) a curative for a fluoroelastomer gum, and(iii) an organo-onium accelerator.
 18. A composition according to claim17 wherein the additive system is present at a level sufficient toimprove the cure rheology of the composition as compared to the curerheology obtained in the absence of the additive system.
 19. Acomposition according to claim 17 further comprising a virginfluoroelastomer gum.
 20. An article comprising the crosslinkedcomposition of claim
 17. 21. A method of recycling an at least partiallyvulcanized fluorinated elastomer comprising the steps of: (a) providinga quantity of the at least partially vulcanized fluorinated elastomer;and an additive system comprising (i) at least one cure-enhancingadditive, (ii) at least one curative, and optionally, (iii) at least oneaccelerator, (b) refining the at least partially vulcanizedfluoroelastomer, (c) blending the additive system with the at leastpartially vulcanized fluoroelastomer, optionally while the at leastpartially vulcanized fluoroelastomer is being refined, and (d) curingthe resulting composition.
 22. A method according to claim 21 whereinrefining the at least partially vulcanized fluoroelastomer occurs in thepresence of a virgin fluoroelastomer gum.
 23. A composition comprising(a) a virgin fluoroelastomer gum, and (b) an effective amount ofadditive system comprising (i) a cure-enhancing additive, (ii) acurative, and (iii) an accelerator.